RFC: LED Line Display (LLD) moving display

[KnorkFox]

Id like to write a driver for this new display. Any microcontroller with at least 11 digital outputs could be used to display text on a moving vehicle, like a car or a fast train.
It could display the speed or any other information.

If a line of neopixel, could be updated fast enough, it could be used as simple output option.

The "display" needs to know the speed of the vehicle( roughly) to use the right timing for text rendering. At first, only one charset will be provided.

Slow moving is possible, but you need a camera to be able to see the text. (The controller needs the speed, or the signal "fast enough", to start displaying.

I though about two "lines" with 20 chars each. The second line is optionally, but if used, it will be printed directly after the first line.

What do you think? Could it be implemented? Have you additional ideas to improve it? I like to hear it.

Fox

[peterhinch]

I saw a demo a very long time ago where a single column of LED's was mounted on top of a vibrating mechanism. Characters were displayed using persistence of vision. This had the benefit of repetition.

I'm unclear whether you intend to use persistence of vision in a similar way. If so, repetition would be absent - I'm not sure whether this would actually work.

[KnorkFox]

this could be tested. I am not completly sure. Thank you, for the reply! It should work for fast moving trains and cars. If they move slow, you need a camera with up to 2 seconds exposure time.

One single line, with ( up to) 40 chars input, will be better than my first idea, to split this up into two rows of 20 chars.

[KnorkFox]

Yes, one strip of neopixel will be fast enough for a LLD. 8 to 12 pixel in one vertical orientation are --enough--, the minimum. More LEDs, render the text smoother.

[KnorkFox]

On the left side, it reads from left to right. On the right side, it needs to start from right to left. e.g. leftside: -->micropython
rightside: micropython <--
top: |
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[KnorkFox]

It works. Here is a short demonstration of the principle. Persistence of vision, needs movement.
https://www.youtube.com/watch?v=3dwBGTJiuNw

[KnorkFox]

The orientation of the output is important.
There are left, right, top and center.
Left is a vertical LLD on the left side, of a driving vehicle. Right, is on the right side.
Top, is a horizontal LLD, which is falling down to the ground. Center, is a horizontal LLD at the roof of a car, which is driving towards the observer.

[KnorkFox]

The timing:

30 chars, should be written, under 400ms (50Kmh), under 250ms (100Kmh), under 160ms (200Kmh).
Moving with different speeds, means that the text length gets longer with higher speeds.

A train, with 50 Kmh, needs a second for 14 meters. At 100 Kmh, it is a length of 28 meters, and at the speed of 200 Kmh, it is 56 m.

I propose 3 different timings, for speeds between 40 to 70, 70 to 150 and 150 to 300 Kmh.
Shorter on higher speeds, and a little bit longer on slower speeds. This is the idea...